The invention relates to liquid filtration systems, and more particularly to the provision and control of automatic periodic cleaning of filter elements.
Filter systems, particularly those associated with silt-laden water, often clog with filtrate rather frequently, requiring periodic cleaning. In the past, such cleaning has been provided through backwash or through a flushing process sometimes known as blow-down, involving a rapid rush of unfiltered liquid over but not through the filter mesh element to a blow-down discharge opening, carrying most of the clogging material along and cleaning the filter. This operation, which bypasses the normal filter outlet to dump the filtrate laden liquid as waste, continues for a short period of time, then the blow-down discharge valve is closed and normal filtration resumes. This blow-down type of filter assembly, and systems incorporating a group of such filter assemblies, are the type of filtration systems to which the present invention relates.
Operation of such blow-down cleaning filter systems has previously been cumbersome or inefficient, or the systems have been expensive to set up and maintain. The operation and sequencing of the cleaning cycles has often been performed by hand or electronic systems which were expensive and rather sophisticated, in addition to requiring a source of electricity in sometimes remote locations.